1. Field of the Invention
The subject-matter of the invention is a new biomaterial which contains epithelial cells on microcarriers (MCs), as well as the preparation and use of said biomaterial for preparing a medicament.
2. Description of the Prior Art
Skin consists of the epidermis, the basement membrane and the dermis. The epidermis forms the outer coat. The dermis consists essentially of fibroblasts with additional substances such as, e.g., collagen. The basement membrane essentially contains keratinocytes which are non-differentiated but proliferating. The epidermis essentially contains differentiated keratinocytes wherein the upper layer is horny. It is true that while the degree of differentiation of the cells is increasing, the ability of the cells to proliferate is decreasing. Accordingly, the non-differentiated keratinocytes exhibit the highest proliferation potency.
Burn wounds and slow-healing wounds (ulcers) usually are treated with skin sheets consisting of autologous keratinocytes (classical method). To this end, a piece of skin is cut off from the patient, the keratinocytes are cultured in vitro, and the expanded skin sheets so obtained are transplanted [Gallico, G. G., et al., New Engl. J. Med. 311 (1984) 448-451 (1); Cuono, C., et al., Lancet (1986) 1123-1124 (2); De Luca, M., et al., Burns 15 (5) (1989) 303-309 (3); Gallico, G. G., Clinics in Plastic Surgery 17 (3) (1990) 519-526 (4); De Luca, M., and Cancedda, R., Burns 18 (1) (1992) 5-9 (5)]. The transfer of thin skin sheets from cell culture flasks to, e.g., Vaseline gauze as well as the fixing thereof onto the wound surface is problematical. The covering of wounds on parts of the body that are difficult to reach is another problem. Besides this, only keratinocytes can be transferred by means of such classical skin sheets. Skin sheets from keratinocytes involve the drawback that these cells are almost completely differentiated when the sheets are being formed, which means that the sheets practically no longer contain any keratinocytes capable of proliferation. Thus, these sheets constitute a transplantation material which cannot grow, or continue growing, after transplantation. Epidermal transplants (classical skin sheets) with allogenic keratinocytes have been carried out in a number of clinics without any immunological rejection reactions being observed (Gboyse, S. T., et al., Plast. Reconst. Surg. 91 (1993) 632 (17); Burt, A. M., et al., Br. Med. J. 298 (1989) 915 (18); Hickerson, W. L., et al., Burns 20/1 (1994) 52 (19)).
From WO 92/06179 (6) and EP-A 0 242 270 (7) biomaterials are known which contain epithelial cells within a collagen gel. In this context, epithelial cells (fibroblasts or keratinocytes) are embedded in gel layers. It is known that such gels may also contain keratinocytes. However, the keratinocytes in the gel are immobilized and are thus incapable of proliferating and differentiating to an appreciable extend after transplantation. Accordingly, keratinocytes from such gels are not able to form a basement membrane and an epidermis. Another drawback of this biomaterial is, in particular, the low rate of migration of the epithelial cells from the biomaterial into the wound. Furthermore, the handling and fixing of these biomaterials is very difficult and laborious.
In WO 90/02796 (8) there is described a three-dimensional cell culture system on the basis of, for instance, cellulose, polyamide, polyester, on which epithelial cells can grow. In this context, an artificial tissue is obtained which is covered with epithelial cells (fibroblasts or keratinocytes) and which is said to be suitable for transplantation. These artificial transplantation materials, too, do not exhibit any advantage over the skin sheets applied in the classical method.